Various arrangements have been proposed and utilised in order to anchor implant devices firmly in place, from suturing (consider, for example, the attachment of prosthetic cardiac valves), to retention effected by the expansion of the device in situ (one typically thinks of stents for angioplasty), to the deployment of mechanical attachment elements.
All of these above-described arrangements have greater or lesser disadvantages.
Attachment by means of suturing nearly always requires accessibility to the implant site from the outside and it is therefore practical only during surgery. Anchorage by way of expansion in situ carries the risk of the subsequent collapse of the device and is therefore practical only where particular conditions exist for the geometric coupling between the device and the associated implant site. Even mechanical attachment such as that utilised, for example, for pacemaker electrodes, often requires direct access to the implant site from the outside. Where implantation is preceded, for example, by catheterisation, the risk exists that attachment may occur before the device has reached the desired implantation site, locking the device itself in an undesirable position, when it can often be dangerous, if not impossible, to remove or reposition it.